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Siple Dome Glaciology and Ice Stream History 1994, 1996

Summary

The Siple Dome Glaciology and Ice Stream History project was part of Western Divide West Antarctic Ice Cores (WAISCORES), an NSF-funded project to understand the influence of the West Antarctic ice sheet on climate and sea level change. WAISCORES researchers acquired and analyzed ice cores from the Siple Dome, in the Siple Coast region, West Antarctica.

This project supported glaciological studies of Siple Dome and its
surroundings between Ice Streams C and D, via two major goals. First, it sought to characterize the dynamic environment and ice stratigraphy of Siple Dome and its surroundings, with
the specific mission of assessing Siple Dome as a potential deep core
site; and second, to determine whether the configuration of ice stream
flow in the region has changed over time. Both goals are relevant to understanding the dynamics of the West Antarctic
Ice Sheet (WAIS), its history, and potential future behavior.

This project was a collaboration between Saint Olaf College, the University
of Washington, and the National Snow and Ice Data Center at the University of Colorado. It included studies of satellite imagery and
acquisition and analysis of field data from GPS, firn cores and snow
pits, and ground-based ice-penetrating radar.

Data in this collection were obtained during two Antarctic field seasons in 1994–95 and 1996–97. The data set is available via FTP as Microsoft Excel Spreadsheet (.xls) and ASCII tab delimited (.txt) files. Related notes are available as a Microsoft Word (.doc) or text (.txt) file. Related images and charts are available as Graphics Interchange Format (.gif) and Joint Photographic Experts Group (.jpg) files.

Citing These Data

We kindly request that you cite the use of this data set in a publication using the following citation. For more information, see our Use and Copyright Web page.

The following example shows how to cite the use of this data set in a publication. List the principal investigators, year of data set release, data set title and version number, dates of the data you used (for example, 1996), publisher: NSIDC, and digital media.

File Size

Spatial Coverage

Spatial Coverage Map

Siple Dome Radio Echo-Sounding Survey Locator Map

Temporal Coverage

Data were obtained during two Antarctic field seasons (November to February) in 1994–1995 and 1996–1997.

Parameter or Variable

Parameters in this data set include local coordinates, using a Lambert projection centered at the summit of Siple Dome (-81.65434,-148.8081,623.23), geographic coordinates (latitude and longitude), distance from the Siple Dome summit, surface elevation, and bed elevation. Table 3 describes the columns and derivation techniques for data in the sdmdata.txt and sdmdata.xls file:

Table 2. Parameter Descriptions for the
sdmdata File

Column

Column Title

Description

Derivation Notes

A, B

Lambert
(-NS and -EW)

Local coordinates using a Lambert projection centered at the summit of Siple Dome (-81.65434,-148.8081,623.23)

The 1610 xy points corresponding to the location of radar waveforms points were derived by interpolation at intervals of ~ 100m from a set of 69 static Global Positioning System (GPS) surveys of poles located along the traverse.

C, D

Latitude and Longitude

Geographic Coordinates

Coordinates were taken from the continuous kinematic GPS data set along the traverse with spacing of ~ 70m. Since the location of these points does not correspond exactly with that of the radar waveforms, a program was written to select the closest set of lat/long coordinates for each radar waveform. Thus, these are all measured (not interpolated) data points. However, there were 2 sections for which there were no kinematic GPS data. For these intervals to which no lat/long coordinates could be assigned, the latitude and longitude were both set to 0 (entries 1024-1043 and 1149-1317).

Data were obtained by calculating the distances between successive sets of Lambert coordinates, and then summing them and adjusting the running distance to be referenced to the summit.
Note: Columns 5, 7, and 9 are identical, repeated for graphing purposes.

F

HAE - surface

Elevation of the surface of Siple Dome in height above ellipsoid (HAE)

Data were obtained from the continuous kinematic GPS. The same procedure used in columns 3 & 4 for selection of the closest kinematic GPS value to a radar waveform was used. However, in the intervals where there were no GPS data (see above), the elevations were linearly interpolated between the 2 endpoints of each gap

H

HAE - bed

Elevation of the bed of Siple Dome in HAE

At each of the 1610 points, the 2-way travel time of the radar signal was determined by picking the mid-point time between the maximum and minimum phase of the bed-echo wavelet. These times were converted into depth using a measured average speed of 1.74040e8 m/s. These depths were then subtracted from the surface elevations.

J

Power (mV^2/sample)

Bed reflection power

Bed reflection power as computed from the square of the amplitude integrated over the echo.

Related Data Collections

4. Data Acquisition and Processing

Data Acquisition Methods

The Siple Dome Glaciology and Ice Stream History project involved two field seasons (November to February) at Siple Dome, the first in 1994–1995 and the second in 1996–1997. During the first season, ice-penetrating radar experiments were undertaken to study the bedrock topography and internal stratigraphy in the vicinity of the summit region to determine its suitability for deep ice coring. An 80 km radar traverse was completed across the north flank of the dome to gather similar data. This traverse was extended across a "scar" feature seen in satellite imagery and hypothesized to be a former shear margin from a relict ice stream. Strain grids were emplaced in the vicinity of the summit and scar regions, and shallow cores were recovered near the summit to measure snow accumulation rates.

Field work during the second field season extended the radar traverse across the southern flank of Siple Dome to complete depiction of bed topography and ice internal stratigraphy. Radar studies to the South also investigated a series of former margin scars of Ice Stream C. Strain grids were resurveyed, and an additional radar traverse with higher resolution was completed across the north flank and scar.

The two field seasons yielded data sets on ice thickness and internal stratigraphy along a traverse from one margin of the dome to the other, as well as a more detailed study of the summit region. Related work done principally by project collaborators resulted in data sets of surface topography and ice velocity, including strain rates in the vicinity of the summit and north scar.

Processing Steps

These data were processed to extract information about ice flow and history in the vicinity of the dome and near its margins. Radar profiles were analyzed to determine ice thickness and bed topography. Enhancements were made to better depict internal stratigraphy and gain information about the nature of the bed. Information from the strain grids was used together with depictions of the internal stratigraphy by our colleagues at the University of Washington to model ice flow in the vicinity of the divide and on the dome flanks. Together, these studies have been used to interpret ice dynamics and history in the vicinity of Siple Dome in an effort to better understand the evolution of the West Antarctic Ice Sheet.